1. Field of the Invention
The present invention relates to an information processing apparatus and an information processing method. In particular, the present invention relates to an information processing apparatus and an information processing method, which are suitably used when editing video data compressed using inter-frame prediction.
2. Description of the Related Art
In an image compression system typified by MPEG (Moving Picture Coding Experts Group/Moving Picture Experts Group) or the like, a video signal is compression-coded using the inter-frame prediction to achieve high compression efficiency. In images that are compressed using the inter-frame prediction, however, frames are interrelated because of prediction, making it difficult to edit video. That is, it is difficult to splice video materials together when video signals thereof are in a compressed state. Therefore, in a system which is expected to edit the video materials, encoding is generally performed using only intraframe compression without using the inter-frame prediction.
However, in the case where a high-definition video signal with a large amount of information, such as an HD (High Definition) signal, is handled, for example, encoding using only the intraframe compression results in low compression efficiency, and therefore demands an expensive system having a high transfer rate, large storage capacity, or a high processing rate to transfer or accumulate a large amount of data. Therefore, in order to handle the high-definition video signal with a large amount of information using an inexpensive system, it is necessary to increase the compression efficiency by using the inter-frame prediction.
In order to edit MPEG streams, a technique is currently employed of once decoding pictures near an edition point (i.e., a splicing point), then splicing resulting uncompressed image signals together at the splicing point, and thereafter encoding the signals again (see, for example, PCT Patent Publication No. WO99/05864).
In MPEG, a compression coding system using bidirectional inter-frame prediction using I pictures, P pictures, and B pictures is called a “Long GOP (Group of Pictures) compression system”.
The I picture is an intra-frame coded picture, i.e., a picture coded without reference to any other picture. Decoding of the I picture is possible without using any other information. The P picture is a forward-predicted, inter-frame coded picture, i.e., a forward-predicted coded picture expressed by a difference from a previous (in terms of time) frame (arranged in a forward direction). The B picture is a bidirectionally predicted coded picture, i.e., a picture coded by motion-compensated inter-frame prediction using a previous (in terms of time) picture (arranged in a forward direction), or a subsequent picture (arranged in a reverse direction), or both the previous and subsequent pictures (arranged in the forward and reverse directions).
Because the P picture and the B picture are lower in data amount than the I picture, it is possible to increase a compression ratio of video by increasing the length of a GOP (i.e., increasing the number of pictures that constitute a long GOP). Therefore, the P and B pictures are suitable for use in digital broadcasting, a DVD (Digital Versatile Disk) Video, or the like. However, when the GOP is too long, edit control with frame-by-frame precision becomes difficult, causing an operational problem in business-purpose edition in particular.
With reference to FIG. 1, an editing process of splicing two pieces of video data compressed in accordance with the Long GOP system together at a specified splicing point will now be described below.
First, each of to-be-edited compressed video data 1 and to-be-edited compressed video data 2 is partially decoded near a splicing point to obtain partial uncompressed video signals 1 and 2. Then, the uncompressed video signals 1 and 2 are spliced together at the splicing point, and the resulting signal is subjected to application of an effect near the splicing point as necessary, and encoded again. Then, the resulting re-encoded compressed video data is combined with the remaining parts of the original compressed video data (i.e., the other parts of the original compressed video data than the parts thereof near the splicing point which have been partially decoded), which have not been subjected to the decoding and re-encoding.
The method described above with reference to FIG. 1 has an advantage over a method of decoding the whole of the to-be-edited compressed video data, splicing the resulting video signals together at the splicing point, and encoding the resulting video signals in its entirety again to obtain edited compressed video data in that degradation of image quality resultant from re-encoding can be limited to a local region and that a time demanded for the editing process can be shortened significantly.